A piston reciprocating in a cylinder bore of an internal combustion engine has a plurality of ring grooves (for example, three ring grooves). For example, two compression rings (chiefly, a first ring that seals a combustion gas and a secondary ring that seals the combustion gas and adjusts a lubricant film) used to prevent a combustion gas from blowing through and an oil ring consisting of a plurality of components (i.e., two rail rings and an expander ring) to adjust the lubricant film are fitted in these ring grooves. A connecting rod is swingably connected to the piston.
As a conventional ring-installing device for installing especially the oil ring among these piston rings, there is known an installation device made up of a magazine that holds a plurality of rings (rail rings) by stacking up the rings in a vertical direction; a ring extruding mechanism made up of a first slide member that is driven in a horizontal direction in order to horizontally extrude a ring occupying the lowest position among the rings stacked up on the magazine, a second slide member that is carried on the first slide member and is driven in an oblique direction, and an extruding member fixed to the second slide member; a ring guide member (ring nest member) that guides the extruded ring to a predetermined position in the horizontal direction and that includes a plurality of tabular members driven and reciprocated synchronously in a radial manner; a ring diameter extending member including a plurality of ring expanding fingers driven and reciprocated synchronously in a radial manner in order to extend the diameter of the ring set at the predetermined position; and a piston holding member that holds the piston at a predetermined position and that is driven and reciprocated in upward and downward directions together with the ring diameter extending member (see U.S. Pat. No. 5,404,629, for example).
However, in the conventional installation device, a reaction force produced when the extruding member of the ring extruding mechanism extrudes the ring acts obliquely with respect to a direction in which the second slide member is slid, i.e., acts to deviate slide surfaces facing in parallel with each other from the mutually parallel state. Therefore, there is a risk that functional reliability will be lowered. Additionally, the extruding member is positionally adjusted to the lowest ring by driving the second slide member in the oblique direction, and, in addition, the influence of a time-dependent change is caused by the action of the reaction force. Therefore, there is a risk that positioning cannot be performed with high accuracy.
Additionally, in the conventional installation device, the ring guide member and the ring diameter extending member are radially reciprocated, and hence the structure becomes complex, and the device is increased in size.
Still additionally, when the ring R is fitted into the ring groove G of the piston P, the ring R guided by the ring guide member 1 to the predetermined position in the horizontal direction is expanded by the ring expanding finger 2 as shown in FIG. 1A to FIG. 1C, and the piston P is placed on the holding member 3. The holding member 3 and the ring expanding finger 2 are then lowered together by a predetermined amount. As a result, the ring R is elastically recovered, and the diameter of the ring R is narrowed so that the ring R can enter the ring groove G.
At this time, a space above an interval between the ring guide member 1 and the piston P is not constrained and is free. Therefore, there is a risk that the ring R will be disengaged from the ring groove G as shown in FIG. 1C, and cannot be reliably fitted thereinto when the ring R is shaped like a wave.
The present invention has been made in consideration of the circumstances of the conventional technique. It is therefore an object of the present invention to provide an installation device and an installation method for a piston ring capable of reliably fitting a piston ring into a ring groove of a piston while simplifying the structure of the device so as to reduce the size thereof.